A connection device of this type is known from EP 0 733 844 B1. In EP 0 733 844 B1, the insert part consists of a one-piece plastic molding which, for the purpose of the releasability of the plugged-in plug portion detained by the clamping ring against being pulled out and formed by one line end, has two elastic latching arms which engage radially with latching extensions into the basic part and into latching orifices formed there. Each latching arm has an actuation portion projecting outward from the basic part. Consequently, the insert part can be released from the basic part, so that the plug portion, with the clamping ring seated on it, can then also be removed jointly with the insert part. Although very simple manual release is possible here, the projecting actuation extensions of the latching arms may nevertheless cause an obstruction or even lead to unwanted release. Moreover, the type of latching at the insert part during assembly requires an exact alignment in the circumferential direction, so that the latching extensions can be introduced correctly into the latching orifices.
A further connection device of the generic type is described in the publication DE 202 14 847 U1. In DE 202 14 847 U1, the insert part can be plugged completely into the basic part. For latching, the insert part has on its outer circumference radial latching extensions which latch radially in each case into a corresponding latching orifice of the basic part. The latching orifices are in this case designed as radial through orifices, so that, for release, the latching extensions can be reached from outside by means of a suitable tool and be moved radially inward, with the result that the plug portion, together with the clamping ring and with the insert part, can be removed. Although high reliability against unwanted release is achieved here, release is in this case nevertheless possible only by means of a suitable auxiliary tool. Moreover, even here, on account of the configuration of the insert part, assembly is possible only in a defined rotary orientation.